When a compound having a dicarboximide skeleton, such as a cyclic imide compound or a cyclic acylurea compound, is used as a catalyst, various radical reactions satisfactorily proceed on various substrates to thereby yield a variety of useful organic compounds efficiently under mild conditions (Patent Documents 1 to 6). By oxidizing a compound having an alkyl group bonded to an aromatic ring, for example, with oxygen in the presence of this catalyst, the alkyl group is efficiently oxidized, and thus an aromatic carboxylic acid such as terephthalic acid or pyromellitic acid can be industrially efficiently produced. By oxidizing a non-aromatic cyclic hydrocarbon such as cyclohexane with oxygen in the presence of the catalyst, an alcohol, a hydroperoxide, or a ketone with hydroxyl group, hydroperoxy group, or oxo group introduced into carbon atom constituting the ring is obtained in a good yield; or a corresponding dicarboxylic acid where the ring has been oxidatively cleaved may be obtained in a good yield under some reaction conditions.
A reaction product obtained by using the catalyst may contain impurities derived from the catalyst or a denatured derivative (deactivated derivative) of the catalyst, and the quality of product may therefore be degraded. In particular, when a compound as a material for a polyester or polyimide, such as terephthalic acid or pyromellitic acid, contains such catalyst-derived impurities, there may occur disadvantages such as inhibition or polymerization reaction and coloring of a produced polymer, because the impurities generally contain nitrogen atom.    Patent Document 1: Japanese Unexamined Patent Application Publication (JP-A) No. 08-38909    Patent Document 2: Japanese Unexamined Patent Application Publication (JP-A) No. 09-327626    Patent Document 3: PCT International Publication Number WO 02/40154    Patent Document 4: Japanese Unexamined Patent Application Publication (JP-A) No. 2003-128618    Patent Document 5: PCT International Publication Number WO 03/28884    Patent Document 6: PCT International Publication Number WO 03/55600